Thermal ink jet printers use ink pens containing printheads and ink cartridges, the printheads having heating elements on a semiconductor substrate for heating ink so that the ink is imparted with sufficient energy to cause the ink to be ejected through one or more nozzle holes in a nozzle plate attached adjacent to a semiconductor substrate. The nozzle plate typically consists of a plurality of spaced nozzle holes which cooperate with individual heater elements on the substrate to eject ink from the cartridge toward the print media. The number, spacing and size of the nozzle holes influences the print quality. Increasing the number of nozzle holes on a printer cartridge typically increases the print speed without necessarily sacrificing print quality. However, there is a practical limit to nozzle hole or orifice size and to the size of the semiconductor substrate which can be produced economically in high yield. Thus, there is a practical limit to the number of corresponding nozzle holes which can be provided in a nozzle plate for a printhead.
For color printing applications, the three primary colors of cyan, magenta and yellow are used to create a palette of colors. In one ink pen design all three colors are provided by a single ink jet pen containing a single semiconductor chip and a single nozzle plate attached to the chip. However, this results in relatively slow print speeds because each color swath is small due to the size of the portion of chip being used for that color. In order to obtain suitable substrate production yields, the semiconductor chips cannot be large enough to contain the same number of energy imparting devices as would be found on individual printheads for each color.
In an effort to increase printing speed, separate ink pens each containing a semiconductor chip, nozzle plate attached to the chip and ink cartridge are provided for each color. In such a design, the number of nozzle holes per color is maximized for high quality, higher speed printing. However, it is extremely difficult to maintain an alignment tolerance of a few microns between the individual ink pens.
While locating multiple individual substrates of a conventional size on the same ink pen body may allow a relatively faster printing rate, such a design contributes to significantly increasing the printhead temperatures because of the greater number of energy imparting devices located on the printhead and the desire to eject the ink from the pen at a faster rate. Increased printhead temperatures cause problems with ink ejection due to viscosity changes in the ink which may result in oversize ink droplets and well as premature ejection of ink from a nozzle hole. Higher temperatures may also contribute to air bubble formation in the ink chambers of the printhead which air bubbles inhibit ink droplet formation. Plugging of the nozzle holes by a build up of ink decomposition products adjacent the nozzle holes may also be a problem caused by higher printhead temperatures. Furthermore, without adequate temperature control, dimensional changes in the printhead are not predictable making it difficult to achieve the desired dot placement which adversely affects print quality.
Various materials and methods have been proposed for removing heat from the printhead substrates. For example, U.S. Pat. No. 5,084,713 to Wong describes flowing ink from the reservoir through a support panel for the heater substrate to cool the printhead. Such a design requires an adequate flow of ink to the printhead in order to remove sufficient heat therefrom.
U.S. Pat. No. 5,066,964 to Fukuda et al. describes the use of flowing ink in combination with a heat capacity member to remove ink from the printhead in order to cool the printhead. U.S. Pat. No. 5,657,061 to Seccombe et al. describes the use of a heat exchanger in the ink flow path to cool the ink and thus cool the printhead as the ink flows to the substrate. Other methods of removing heat include the use of a heat pipe and blower as described in U.S. Pat. No. 5,451,989 to Kadowaki et al.
Conventionally, materials which exhibit a low thermal expansion coefficient have been used to provide suitable heat removal without sacrificing print quality. Materials having low thermal expansion coefficients do not typically expand or contract a sufficient amount to affect printer operation and thus print quality. The materials also enable easier and cheaper ink jet pen and cartridge fabrication techniques since expansion and/or contraction of the components and electrical connections therebetween are minimized. However, such low thermal expansion materials are typically made from exotic composites such as metal-ceramic mixtures, carbon fiber, or graphite composites which are costly to make and use in such applications.
Heat conductive metals have typically not been used in ink jet pen applications because of difficulties encountered with protecting the metal surfaces from ink corrosion which results when ink mist and non-dried ink on the print media come into contact with the nozzle plate and ink pen body surfaces. Over time, the ink can sufficiently corrode metal surfaces thereby affecting pen life and print quality. Materials which may adequately protect metal surfaces from ink corrosion have had disadvantageous effects on the ability of adhesives used in the assembly of the pen to adhere to the protected surface thereby rending such treatment materials ineffective.
Accordingly, there is a continual need in the art for improved ink jet pen components, particularly ink pen bodies, which effectively dissipate heat and are resistant to the corrosive effects of ink.